Many consumer products now provide the facility to reproduce digitally encoded data, examples of such consumer products including personal stereos (such as MP3 players), mobile phone handsets, video conferencing facilities, digital and cable television and desktop computers. The digital data may be provided in the form of pre-recorded data retrieved from a storage medium, such as a CD, DVD or CD-ROM.
As will be appreciated by those skilled in the art, the amount of digital data required to record and/or transmit any given data item will vary depending upon a number of factors. However, for the stored or transmitted data to be reproduced some form of compression of the data is typically required to facilitate storage/transmission. In an effort to ensure a minimum standard of data transmission and data quality is provided to the consumer and to also try to ensure a maximum degree of interoperability between different manufacturers' equipment, a number of industry standards have been developed specifying the parameters to which the data compression must comply. Examples of such standards include H.264/AVC, MPEG-4, MPEG-2, H263+, H263 and H.261.
A common feature of the above-mentioned compression standards is that the compression, and hence the decompression, of any given data segment (the definition of what constitutes a data segment varying in dependence on the data type e.g. for video data a segment may comprise an individual frame) often utilises data from one or more previous data segments. Whilst it is known to perform a number of tests and data analysis procedures to ensure compliance of a newly developed encoder and/or decoder to the standards and interoperability with other vendors' compression algorithms, these procedures yielding valuable data concerning the performance of the newly developed encoder/decoder, the decompressed data itself generated by the decoder is rarely saved and is thus not available for subsequent analysis. This is because, in general, the amount of data memory required to store the decompressed data is prohibitive, this being one of the main reasons for the data being compressed initially. Consequently, one function that is difficult to provide without the use of large amounts of memory is that of rewinding or stepping back through the decompressed data a segment at a time.
It is known in the prior art to provide data analysis tools or players that allow a user to re-start the data playback from a previous point. This is possible only if the data stream includes an appropriate number of ‘entry points’, which are points in the data stream that require no previous information to allow decoding to resume. For video data such entry points typically occur at the beginning of different scenes, thus allowing a user to step-back through the video data a scene at a time. However, this scheme does not allow a frame by frame rewinding of the video data that would be more beneficial in detailed analysis. Furthermore, not all video data streams are encoded with such entry points, rendering any kind of rewind or step-back practically impossible.